Most of today's large computer systems need provisions for rapid, low cost trouble shooting of hardware failures in the system. Some have complex arrangements of switches and display apparatus connected with the logic of the unit itself for switching in data, addresses and commands and displaying internal conditions in the machine. Typically these maintenance panel arrangements allow a field engineer to read data from and write data to registers and memory locations, to supply addresses, set fault conditions, set flags, control display functions, check the condition of various control points, check the status of the system and, in general, trace functioning of the system through each step of each machine instruction. Prior art maintenance panels sometimes consisted of long strings of toggle switches for entering data and addresses, and long strings of LED indicators for display of data. Separate command switches were generally required to select timing margins, select the registers or control points to be displayed and to cause the processor to execute commands set into the data switches or enter a single step mode. Entering data, commands and addresses via the prior art maintenance panels, and displaying data relating to the performance of the machine using these prior maintenance panels was time consuming and cumbersome.
Servicing computer systems is now the fastest growing segment of the computer industry according to a recent article in Business Week. A major reason is the spread of distributed processing which is resulting in computer hardware located everywhere. With computer terminals spread throughout a company, very often the data processing system is the central nervous system of the organization. Computer users are now very often less concerned with price performance ratios than with service turnaround time.
The testing apparatus disclosed herein, is designed to replace prior art maintenance panels with microprocessor technology to streamline field engineering and reduce the manufacturing cost of data processing units in which the testing apparatus is incorporated. The system disclosed is incorporated into the structure of the central processing unit or other unit in the data processing system, and has an external interface for control of the testing apparatus from the external world. The preferred embodiment can be controlled from either a portable maintenance panel held in the hand of a field engineer or from a computer terminal located in the vicinity of the tested unit or from a computer terminal located anywhere in the world and coupled to the testing apparatus via a communications network. The possibility exists for interface of the testing apparatus to another digital computer programmed to run a predetermined series of tests on the tested unit from a centrally located field engineering office for rapid and accurate pinpointing of defects in the tested unit. The disclosed testing apparatus thereby enables the mainframe computer manufacturer to maintain a staff of highly trained maintenance specialists in a central location close to the manufacturing plant with the capability of servicing computer systems all over the world. This enhanced maintenance capability both decreases field engineering costs enabling lower hardware costs to the customers, and provides better maintenance support to those customers.